The present invention relates to a fastening device for fastening two separate members with each other with a relative interval between them.
Conventionally, the fastening devices for fastening two members with a relative interval between them have been already disclosed in the technical field of automobile and the like. For example, Japanese Patent Application Laid-Open No. 2002-347656 has disclosed a fastening device comprising a sleeve welded on one component of the two separate members, a spacer screw-fastening with the sleeve through an inverse screw and a bolt having a male screw portion capable of screw-fastening with a female screw portion formed in the spacer at a front end of a shaft portion.
The male screw portion of the bolt of this fastening device is coated with adhesive agent capable of transmitting a predetermined torque to the spacer and when the bolt is tightened, the spacer is rotated due to a transmission torque, so that it is pulled out from the sleeve. However, because if the spacer comes into a contact with the other member, it cannot rotate further, the male screw portion formed at the front end of the bolt is released from the female screw portion and advanced so as to screw-fasten with the female screw portion of the sleeve, so that the two members are fastened with each other with an interval by the spacer. To allow the bolt to be advanced quickly at this time, it is preferable to obtain a structure capable of passing through the female screw portion of the spacer without rotating the shaft portion of the bolt.
Because such a bolt is produced at the front end portion of a cylindrical blank according to the method of rolling the male screw portion, the root diameter of the male screw portion is formed smaller than the blank diameter (diameter of a cylindrical portion) of the bolt. Thus, because the inside diameter of the female screw portion of the spacer which screw-fastens with the male screw portion is smaller than the diameter of the cylindrical portion of the bolt, the cylindrical portion of the bolt cannot pass through the female screw portion of the spacer. Thus, the cylindrical portion of the bolt needs to be reduced in diameter by additional processing such as cutting processing and plastic deformation so that it is capable of passing through the female screw portion of the spacer. For the reason, processing steps for the bolt increases and further, manufacturing cost rises.